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Current Insights On First MPJ Implants

Tuesday, 03/29/11 | 34755 reads

What About Emerging MPJ Implants?

There are also similar and modified designs that recently obtained FDA approval. The Metatarsal Decompression Implant (Solana Surgical) has a cantilever stem, which is angled between 45 and 75 degrees. This appears to facilitate a more anatomical design.

The Anatoemic Phalangeal Prosthesis (Arthrex) received FDA approval in 2007 but limited data has been published on this device. OsteoMed has two systems with the EnCompass Metatarsal Resurfacing device and a classic Hemi™ Great Toe Implant. Both systems are press-fit and appear similar to previous designs.

Recent years have seen the rise of innovative implants for first metatarsophalangeal joint (MPJ) pathologies. Accordingly, this author offers an intriguing review of the current literature on first MPJ arthroplasty.

Over the past decade, there have been steady improvements for first metatarsophalangeal joint (MPJ) pathologies. These include first MPJ hemi-implants, resurfacing of the first MPJ and two- or three-component implants. With the growing number of companies entering the foot and ankle market, it can be overwhelming to keep up with such data and material. Accordingly, let us take a closer look at the literature on these implants.

Metatarsophalangeal joint implants have been adjunctive treatments for the podiatric physician for over 60 years. After decades of design improvements, material enhancements, biomechanical studies and a better understanding of patient candidacy, the ideal implant is still under question. Aside from improvements in design and materials, the greatest factor has been the quality of controlled trials available for the foot and ankle surgeon to assist in decision making. There is still a lack of quality level 1 or 2 evidence-based medicine (EBM) studies. However, level 3 and 4 EBM studies can be valuable tools.

When discussing the first MPJ, it is essential to have a strong understanding of the different pathologies and proper indications for implant use. Drago and colleagues developed one of several grading classifications.1 This classification includes four different stages.

Surprisingly, the option of joint arthroplasty is not in the currently published clinical practice guidelines.2 As of September 2009, the Academy of Ambulatory Foot and Ankle Surgery did not include the use of any type of implant alone for either hallux limitus or hallux rigidus. Keller arthoplasty in conjunction with an implant is the final recommendation before first MPJ fusion. However, in the past 10 years, there have been 15 medical device companies that have filed a patent pending for their design of a first MPJ implant and there has only been one recall.3

Assessing The Study Results For The BioPro Great Toe Hemi-Implant

Great Toe Hemi-Implant (BioPro). In 1994, Townley and Taranow reviewed the use of a metallic resurfacing hemiarthroplasty in 279 cases over a 40-year period.4 Indications for surgery included hallux rigidus, rheumatoid arthritis and degenerative changes associated with hallux limitus and bunion deformity. The study authors noted that follow-up, which ranged from eight months to 33 years, showed good to excellent results in 95 percent of the cases.

In 2010, Salonga and colleagues reviewed 79 first MPJ hemiarthroplasties in 23 men and 53 women.5 The mean age of the patients in the study was 59.6 years of age and the mean follow-up was 2.91 years. The indications for implantation were failure of conservative treatment, chronic first MPJ pain, degenerative osteoarthritis of the first MPJ and decreased ambulation and functional status. The advantages included minimal postoperative debilitation and reliable pain relief, according to the authors.

The mean postoperative American College of Foot and Ankle Surgeons (ACFAS) Universal Evaluation score was 94.00.5 The researchers found statistically significant increases in first MPJ dorsiflexion and plantarflexion. They also saw decreases in the first intermetatarsal angle and metatarsal elevatus but noted that these were unlikely to be clinically significant. Post-op care entailed seven to 10 days in a bandage and post-op shoe with a subsequent return to walking.

In a retrospective article comparing 27 arthrodesis procedures versus 21 hemiarthroplasties, Raikin and colleagues showed that 24 percent of the BioPro Great Toe Hemi-Implant group failed while 100 percent of the arthrodesis group achieved fusion.6 Patients in the hemiarthroplasty group had an American Orthopaedic Foot and Ankle Society-Hallux Metatarsophalangeal Interphalangeal (AOFAS-HMI) score of 71.8 percent whereas patients in the arthrodesis group had an AOFAS-HMI score of 93 percent.6 The BioPro implants showed dorsal subsidence at the final follow-up evaluation (a mean of 79.4 months). Eight of the 16 surviving implants displayed cutout of the distal portion through the plantar cortex of the proximal phalanx on the final follow-up radiographs. However, none were associated with osteolysis.

Roukis and Townley conducted a prospective study intended to report follow-up and analysis of patients who underwent surgical intervention for symptomatic hallux rigidus in the form of either a periarticular osteotomy or a resurfacing endoprosthesis.7 The AOFAS-HMI score increased by 30.2 points, from 54.4 preoperatively to 84.6 postoperatively, for the periarticular osteotomy group. The mean AOFAS-HMI score increased 26.7 points, from 51.1 preoperatively to 77.8 postoperatively, for the resurfacing endoprosthesis group.

What The Research Reveals About Other Implants

Trihedron™ Great Toe Hemi-Implant (Small Bone Innovations). Assessing the use of the Trihedron for hallux rigidus in a series of 23 cases, Sorbie and Saunders noted an average AOFAS score of 88.2 after hemiarthroplasty with an average gain of 31.4 points.8 The design of the implant included a 4-degree angle in the coronal plane to accommodate the shape of the proximal phalanx. The study authors also found no evidence of loosening or osteolysis at the last follow-up evaluation, which took place between 34 to 72 months postoperatively. One disadvantage of the study was it did not discuss range of motion over the past five years.

Futura™ Metal Hemi-Toe implant (Tornier). In 2009, Konkel and colleagues evaluated 23 patients over a six-year period with the Futura Metal Hemi-Toe implant.9 These patients suffered from grade 3 and 4 hallux rigidus, and their average age was 62 years. After assessing the outcome of these patients, the authors noted the patients had an average of 92 percent plantarflexion, average 73 percent dorsiflexion, a total average range of motion of 76 percent and an AOFAS score of 78 percent improvement.

The authors concluded that the Futura Metal Hemi-Toe implant had been used successfully with only mild lucency at the bases of the implants and no clinically visible subsidence on radiographs after an average follow-up of six years.9

HemiCAP® (Arthrosurface). The HemiCAP system addresses hallux rigidus at the metatarsal head. The implant resurfaces damaged articular surfaces and restores the patient’s own unique joint geometry. Over the years, the design has changed and the implant now includes a dorsal lip to reduce osteophyte ingrowth as with the previous design.

Carpenter and colleagues assessed the use of 32 implants in patients with hallux rigidus.10 Seventy-two percent of the study group had grade III hallux rigidus while the remaining 28 percent had grade II hallux rigidus. The average age of patients in the study was 63. The average follow-up was 27.3 months. The preoperative mean AOFAS-HMI score was 30.84 and the postoperative mean was 89.31. No implants were revised or removed, and no loosening occurred.

In July 2009, Hopson and colleagues published a single case report involving a failed HemiCAP implant.11 The authors believe the HemiCAP system does not address the proximal phalanx of the hallux and is still too new to have substantial long-term studies describing its use. Unfortunately, if this implant fails and requires removal, as was the course of events in this case study, a large bone deficit remains in the first metatarsal head.

A Closer Look At EBM And Insurance Coverage For First MPJ Arthroplasty

The National Institute for Health and Clinical Excellence (NICE) published an Interventional Procedure Guidance in 2005 based on an analysis of seven case series.12 The NICE guidance concluded that current evidence on the safety and efficacy of first MPJ replacement of the hallux appears adequate to support the use of first MPJ arthroplasty. However, the guidance also states there is little evidence on the durability of newer implants and that complications may necessitate removal of the joint. These complications include persistent pain, infection, implant loosening, implant fracture, osteolysis, bone over-production, cyst formation, silastic granulomas and transfer metatarsalgia. With the lack of published data, insurance companies have not provided coverage for these devices as they deem them experimental and unproven.

However, when reviewing Cigna’s policies, the company covers partial or total replacement of the first MPJ as a medically necessary alternative to arthrodesis.13 In order to receive coverage from Cigna, patients must have persistent severe disabling symptoms from hallux valgus or hallux rigidus due to degenerative joint disease of the first MPJ, and they must have previously failed conservative medical management. Aetna considers total prosthetic replacement arthroplasty with silastic implants and hemiarthroplasty medically necessary for people with disabling arthritis of the first MPJ and for hallux rigidus. However, Aetna considers other indications experimental and investigational.14

In Conclusion

Most surgeons consider first MPJ implants to be relatively contraindicated in young patients.15 In general, one should avoid joint replacement or resurfacing procedures in young patients as well as those who are required to participate in significant weightbearing activities.

Contraindications to joint replacement include a history of joint or adjacent bone infection, poor bone stock, inadequate soft tissue coverage and a joint that can be preserved by means of osteotomy or other reconstructive options.15

In 2008, Yee and Lau published a current concepts review and determined that most supporting evidence in regard to hemiarthroplasties for hallux rigidus is below Level 3 evidence and long-term consequences for hemiarthroplasties remain uncertain.16

Although there is not consistent scientific evidence available that demonstrates the clinical effectiveness of partial implants, limited data from several studies suggest that MPJ replacement may be a reasonable option for a carefully selected subset of patients.15

Dr. Martins is in private practice in Jackson, Mich., and Adrian, Mich.